Engines used to power mobile and stationary machines generate substantial amounts of heat during operation. Heat, if not properly dealt with, can reduce fuel efficiency and/or cause damage to engine and/or machine components. Such engines typically include cooling systems to remove heat from the engine during operation. The cooling systems may include, among other things, a fan configured to draw heat away from, and/or push cooling airflow toward the engine.
In a typical cooling circuit for an internal combustion engine, coolant passes through a jacket surrounding the engine as the coolant temperature rises. The coolant then passes through the radiator, entering the radiator through a manifold and then passing through cooling tubes where air flows over the tubes to remove heat from and to reduce the temperature of the coolant. The coolant re-circulates via a second manifold back to the engine. Such cooling systems generally have a coolant pump for pumping the coolant through the engine coolant circuit. A valve prevents coolant from circulating through the radiator while the engine is warming up. The engine fan draws air through the radiator to remove heat from the coolant.
Many engines are equipped with a single-speed fan. Typical control methods for cooling such engines may be based on coolant temperature. A controller may instruct various actuators to open or close the coolant valve and switch the fan on and off. The speed of the coolant pump may also be controlled.
However, due to varying conditions, which may be environmental or workload based, it may be beneficial to run the fan at a variable speed. For example, an on-highway truck hauling a load up a steep incline on a hot summer day may require more cooling than the same truck idling at a stop on a cold winter day. While it may be necessary and/or efficient to run the fan at a high speed under the former circumstance, it may be unnecessary and/or inefficient to run the fan at the same high speed under the later circumstance. As such, there is a need to regulate or control fan speed in response to changing environmental or workload conditions.
Control of an engine fan may provide a number of benefits. For example, a properly controlled engine fan may protect against engine overheating. Further, fan control may improve fuel efficiency by adjusting fan speed to provide only the necessary cooling capacity in response to machine, engine, transmission and environmental conditions. Because an engine fan consumes power from the engine, minimizing the power consumed by the fan will improve fuel efficiency. Further, a properly controlled engine fan helps to regulate emissions as an engine fan may affect the intake manifold air temperature (IMAT), which dramatically affects engine emissions, such as NOx, CO and particulate matter (PM).
As shown in U.S. Pat. No. 7,863,839, an engine fan control system may be based on determining a desired fan speed, making any necessary corrections, and adjusting the fan speed accordingly. The desired fan speed may be determined in response to parameter signals provided by various sensors, such as IMAT, coolant temperature, hydraulic fluid temperature, transmission oil temperature, engine oil temperature, cabin temperature and other parameters. While the fan control system of the '839 patent adjusts the fan speed based on one or more parameters, e.g., coolant temperature, it still takes time for the action of the fan to change the coolant to the desired coolant temperature. Thus, there is a time lag between the determination of the desired fan speed and the desired effect. This time lag may result in certain engine components experiencing thermal fatigue, reduced fuel economy and increased emissions or emission shifting. The time lag problem is also exacerbated in certain machine work cycles where the engine workload and other environmental conditions may change continuously.
For example, when an excavator performs a dig movement or a dig segment of a work cycle, the required engine power increases immediately as well as the heat transferred to the engine coolant. However, it takes time for the coolant temperature to increase. By the time a traditional fan speed controller detects the temperature change and calculates a new desired fan speed, the excavator might already be performing a different segment of the work cycle, such as a swing segment and/or a dump segment. The required engine power decreases during these segments and therefore the cooling requirements decrease, but desired fan speed may remain unnecessarily at a maximum value due to the time lag.
Thus, a need exists for a fan control system and method of controlling an engine fan that overcomes these problems.